From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: Marc Lehmann <schmorp@schmorp.de>, linux-btrfs@vger.kernel.org
Subject: Re: first mount(s) after unclean shutdown always fail
Date: Wed, 1 Jul 2020 09:30:25 +0800 [thread overview]
Message-ID: <36fcfc97-ce4c-cce8-ee96-b723a1b68ec7@gmx.com> (raw)
In-Reply-To: <20200701005116.GA5478@schmorp.de>
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On 2020/7/1 上午8:51, Marc Lehmann wrote:
> Hi!
>
> I have a server with multiple btrfs filesystems and some moderate-sized
> dmcache caches (a few million blocks/100s of GBs).
>
> When the server has an unclean shutdown, dmcache treats all cached blocks
> as dirty. This has the effect of extremely slow I/O, as dmcache basically
> caches a lot of random I/O, and writing these blocks back to the rotating
> disk backing store can take hours. This, I think, is related to the
> problem.
>
> When the server is in this condition, then all btrfs filesystems on slow
> stores (regardless of whether they use dmcache or not) fail their first
> mount attempt(s) like this:
>
> [ 173.243117] BTRFS info (device dm-7): has skinny extents
> [ 864.982108] BTRFS error (device dm-7): open_ctree failed
>
> Recent kernels sometimes additionally fail like this (super_total_bytes):
>
> [ 867.721885] BTRFS info (device dm-7): turning on sync discard
> [ 867.722341] BTRFS info (device dm-7): disk space caching is enabled
> [ 867.722691] BTRFS info (device dm-7): has skinny extents
> [ 871.257020] BTRFS error (device dm-7): super_total_bytes 858976681984 mismatch with fs_devices total_rw_bytes 1717953363968
> [ 871.257487] BTRFS error (device dm-7): failed to read chunk tree: -22
> [ 871.269989] BTRFS error (device dm-7): open_ctree failed
This looks like an old fs with some bad accounting numbers.
Have you tried btrfs rescue fix-device-size?
Thanks,
Qu
>
> all the filesystems in question are mounted twice during normal boots,
> with diferent subvolumes, and systemd parallelises these mounts. This might
> play a role in these failures.
>
> Simply trying to mount the filesystems again then (usually) succeeds with
> seemingly no issues, so these are spurious mount failures. These repeated
> mount attewmpts are also much faster, presumably because a lot of the data
> is already in memory.
>
> As far as I am concerned, this is 100% reproducible (i.e. it happens on every
> unclean shutdown). It also happens on "old" (4.19 era) filesystems as well as
> on filesystems that have never seen anything older than 5.4 kernels.
>
> It does _not_ happen with filesystems on SSDs, regardless of whether they
> are mounted multiple times or not. It does happen to all filesystems that
> are on rotating disks affected by dm-cache writes, regardless of whether
> the filesystem itself uses dmcache or not.
>
> The system in question is currently running 5.6.17, but the same thing
> happens with 5.4 and 5.2 kernels, and it might have happened with much
> earlier kernels as well, but I didn't have time to report this (as I
> secretly hoped newer kernels would fix this, and unclean shutdowns are
> rare).
>
> Example btrfs kernel messages for one such unclean boot. This involved
> normal boot, followed by unsuccessfull "mount -va" in the emergency shell
> (i.e. a second mount fasilure for the same filesystem), followed by a
> successfull "mount -va" in the shell.
>
> [ 122.856787] BTRFS: device label LOCALVOL devid 1 transid 152865 /dev/mapper/cryptlocalvol scanned by btrfs (727)
> [ 173.242545] BTRFS info (device dm-7): disk space caching is enabled
> [ 173.243117] BTRFS info (device dm-7): has skinny extents
> [ 363.573875] INFO: task mount:1103 blocked for more than 120 seconds.
> the above message repeats multiple times, backtrace &c has been removed for clarity
> [ 484.405875] INFO: task mount:1103 blocked for more than 241 seconds.
> [ 605.237859] INFO: task mount:1103 blocked for more than 362 seconds.
> [ 605.252478] INFO: task mount:1211 blocked for more than 120 seconds.
> [ 726.069900] INFO: task mount:1103 blocked for more than 483 seconds.
> [ 726.084415] INFO: task mount:1211 blocked for more than 241 seconds.
> [ 846.901874] INFO: task mount:1103 blocked for more than 604 seconds.
> [ 846.916431] INFO: task mount:1211 blocked for more than 362 seconds.
> [ 864.982108] BTRFS error (device dm-7): open_ctree failed
> [ 867.551400] BTRFS info (device dm-7): turning on sync discard
> [ 867.551875] BTRFS info (device dm-7): disk space caching is enabled
> [ 867.552242] BTRFS info (device dm-7): has skinny extents
> [ 867.565896] BTRFS error (device dm-7): open_ctree failed
> [ 867.721885] BTRFS info (device dm-7): turning on sync discard
> [ 867.722341] BTRFS info (device dm-7): disk space caching is enabled
> [ 867.722691] BTRFS info (device dm-7): has skinny extents
> [ 871.257020] BTRFS error (device dm-7): super_total_bytes 858976681984 mismatch with fs_devices total_rw_bytes 1717953363968
> [ 871.257487] BTRFS error (device dm-7): failed to read chunk tree: -22
> [ 871.269989] BTRFS error (device dm-7): open_ctree failed
> [ 872.535935] BTRFS info (device dm-7): disk space caching is enabled
> [ 872.536438] BTRFS info (device dm-7): has skinny extents
>
> Example fstab entries for the mounts above:
>
> /dev/mapper/cryptlocalvol /localvol btrfs defaults,nossd,discard 0 0
> /dev/mapper/cryptlocalvol /cryptlocalvol btrfs defaults,nossd,subvol=/ 0 0
>
> I don't need assistance, I merely write this in the hope of btrfs being
> improved by this information.
>
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next prev parent reply other threads:[~2020-07-01 1:30 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-01 0:51 first mount(s) after unclean shutdown always fail Marc Lehmann
2020-07-01 1:30 ` Qu Wenruo [this message]
2020-07-01 20:14 ` Marc Lehmann
2020-07-01 23:45 ` Qu Wenruo
2020-07-01 23:55 ` Marc Lehmann
2020-07-02 0:02 ` Qu Wenruo
2020-07-02 1:11 ` Marc Lehmann
2020-07-02 1:28 ` Qu Wenruo
2020-07-02 2:13 ` Marc Lehmann
2020-07-02 18:31 ` Zygo Blaxell
2020-07-03 8:04 ` Marc Lehmann
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